( function () {
class Refractor extends THREE.Mesh {
  constructor(geometry, options = {}) {
    super(geometry);
    this.type = 'Refractor';
    const scope = this;
    const color = options.color !== undefined ? new THREE.Color(options.color) : new THREE.Color(0x7F7F7F);
    const textureWidth = options.textureWidth || 512;
    const textureHeight = options.textureHeight || 512;
    const clipBias = options.clipBias || 0;
    const shader = options.shader || Refractor.RefractorShader; //

    const virtualCamera = new THREE.PerspectiveCamera();
    virtualCamera.matrixAutoUpdate = false;
    virtualCamera.userData.refractor = true; //

    const refractorPlane = new THREE.Plane();
    const textureMatrix = new THREE.Matrix4(); // render target

    const parameters = {
      minFilter: THREE.LinearFilter,
      magFilter: THREE.LinearFilter,
      format: THREE.RGBFormat
    };
    const renderTarget = new THREE.WebGLRenderTarget(textureWidth, textureHeight, parameters);

    if (!THREE.MathUtils.isPowerOfTwo(textureWidth) || !THREE.MathUtils.isPowerOfTwo(textureHeight)) {
      renderTarget.texture.generateMipmaps = false;
    } // material


    this.material = new THREE.ShaderMaterial({
      uniforms: THREE.UniformsUtils.clone(shader.uniforms),
      vertexShader: shader.vertexShader,
      fragmentShader: shader.fragmentShader,
      transparent: true // ensures, refractors are drawn from farthest to closest

    });
    this.material.uniforms['color'].value = color;
    this.material.uniforms['tDiffuse'].value = renderTarget.texture;
    this.material.uniforms['textureMatrix'].value = textureMatrix; // functions

    const visible = function () {
      const refractorWorldPosition = new THREE.Vector3();
      const cameraWorldPosition = new THREE.Vector3();
      const rotationMatrix = new THREE.Matrix4();
      const view = new THREE.Vector3();
      const normal = new THREE.Vector3();
      return function visible(camera) {
        refractorWorldPosition.setFromMatrixPosition(scope.matrixWorld);
        cameraWorldPosition.setFromMatrixPosition(camera.matrixWorld);
        view.subVectors(refractorWorldPosition, cameraWorldPosition);
        rotationMatrix.extractRotation(scope.matrixWorld);
        normal.set(0, 0, 1);
        normal.applyMatrix4(rotationMatrix);
        return view.dot(normal) < 0;
      };
    }();

    const updateRefractorPlane = function () {
      const normal = new THREE.Vector3();
      const position = new THREE.Vector3();
      const quaternion = new THREE.Quaternion();
      const scale = new THREE.Vector3();
      return function updateRefractorPlane() {
        scope.matrixWorld.decompose(position, quaternion, scale);
        normal.set(0, 0, 1).applyQuaternion(quaternion).normalize(); // flip the normal because we want to cull everything above the plane

        normal.negate();
        refractorPlane.setFromNormalAndCoplanarPoint(normal, position);
      };
    }();

    const updateVirtualCamera = function () {
      const clipPlane = new THREE.Plane();
      const clipVector = new THREE.Vector4();
      const q = new THREE.Vector4();
      return function updateVirtualCamera(camera) {
        virtualCamera.matrixWorld.copy(camera.matrixWorld);
        virtualCamera.matrixWorldInverse.copy(virtualCamera.matrixWorld).invert();
        virtualCamera.projectionMatrix.copy(camera.projectionMatrix);
        virtualCamera.far = camera.far; // used in WebGLBackground
        // The following code creates an oblique view frustum for clipping.
        // see: Lengyel, Eric. “Oblique View Frustum Depth Projection and Clipping”.
        // Journal of Game Development, Vol. 1, No. 2 (2005), Charles River Media, pp. 5–16

        clipPlane.copy(refractorPlane);
        clipPlane.applyMatrix4(virtualCamera.matrixWorldInverse);
        clipVector.set(clipPlane.normal.x, clipPlane.normal.y, clipPlane.normal.z, clipPlane.constant); // calculate the clip-space corner point opposite the clipping plane and
        // transform it into camera space by multiplying it by the inverse of the projection matrix

        const projectionMatrix = virtualCamera.projectionMatrix;
        q.x = (Math.sign(clipVector.x) + projectionMatrix.elements[8]) / projectionMatrix.elements[0];
        q.y = (Math.sign(clipVector.y) + projectionMatrix.elements[9]) / projectionMatrix.elements[5];
        q.z = -1.0;
        q.w = (1.0 + projectionMatrix.elements[10]) / projectionMatrix.elements[14]; // calculate the scaled plane vector

        clipVector.multiplyScalar(2.0 / clipVector.dot(q)); // replacing the third row of the projection matrix

        projectionMatrix.elements[2] = clipVector.x;
        projectionMatrix.elements[6] = clipVector.y;
        projectionMatrix.elements[10] = clipVector.z + 1.0 - clipBias;
        projectionMatrix.elements[14] = clipVector.w;
      };
    }(); // This will update the texture matrix that is used for projective texture mapping in the shader.
    // see: http://developer.download.nvidia.com/assets/gamedev/docs/projective_texture_mapping.pdf


    function updateTextureMatrix(camera) {
      // this matrix does range mapping to [ 0, 1 ]
      textureMatrix.set(0.5, 0.0, 0.0, 0.5, 0.0, 0.5, 0.0, 0.5, 0.0, 0.0, 0.5, 0.5, 0.0, 0.0, 0.0, 1.0); // we use "Object Linear Texgen", so we need to multiply the texture matrix T
      // (matrix above) with the projection and view matrix of the virtual camera
      // and the model matrix of the refractor

      textureMatrix.multiply(camera.projectionMatrix);
      textureMatrix.multiply(camera.matrixWorldInverse);
      textureMatrix.multiply(scope.matrixWorld);
    } //


    function render(renderer, scene, camera) {
      scope.visible = false;
      const currentRenderTarget = renderer.getRenderTarget();
      const currentXrEnabled = renderer.xr.enabled;
      const currentShadowAutoUpdate = renderer.shadowMap.autoUpdate;
      renderer.xr.enabled = false; // avoid camera modification

      renderer.shadowMap.autoUpdate = false; // avoid re-computing shadows

      renderer.setRenderTarget(renderTarget);
      if (renderer.autoClear === false) renderer.clear();
      renderer.render(scene, virtualCamera);
      renderer.xr.enabled = currentXrEnabled;
      renderer.shadowMap.autoUpdate = currentShadowAutoUpdate;
      renderer.setRenderTarget(currentRenderTarget); // restore viewport

      const viewport = camera.viewport;

      if (viewport !== undefined) {
        renderer.state.viewport(viewport);
      }

      scope.visible = true;
    } //


    this.onBeforeRender = function (renderer, scene, camera) {
      // Render
      renderTarget.texture.encoding = renderer.outputEncoding; // ensure refractors are rendered only once per frame

      if (camera.userData.refractor === true) return; // avoid rendering when the refractor is viewed from behind

      if (!visible(camera) === true) return; // update

      updateRefractorPlane();
      updateTextureMatrix(camera);
      updateVirtualCamera(camera);
      render(renderer, scene, camera);
    };

    this.getRenderTarget = function () {
      return renderTarget;
    };
  }

}

Refractor.prototype.isRefractor = true;
Refractor.RefractorShader = {
  uniforms: {
    'color': {
      value: null
    },
    'tDiffuse': {
      value: null
    },
    'textureMatrix': {
      value: null
    }
  },
  vertexShader:
  /* glsl */
  `

		uniform mat4 textureMatrix;

		varying vec4 vUv;

		void main() {

			vUv = textureMatrix * vec4( position, 1.0 );
			gl_Position = projectionMatrix * modelViewMatrix * vec4( position, 1.0 );

		}`,
  fragmentShader:
  /* glsl */
  `

		uniform vec3 color;
		uniform sampler2D tDiffuse;

		varying vec4 vUv;

		float blendOverlay( float base, float blend ) {

			return( base < 0.5 ? ( 2.0 * base * blend ) : ( 1.0 - 2.0 * ( 1.0 - base ) * ( 1.0 - blend ) ) );

		}

		vec3 blendOverlay( vec3 base, vec3 blend ) {

			return vec3( blendOverlay( base.r, blend.r ), blendOverlay( base.g, blend.g ), blendOverlay( base.b, blend.b ) );

		}

		void main() {

			vec4 base = texture2DProj( tDiffuse, vUv );
			gl_FragColor = vec4( blendOverlay( base.rgb, color ), 1.0 );

		}`
};

THREE.Refractor = Refractor;
} )();
